Very high frequency superheterodyne receiver with self-oscillating mixer



1965 K. H. KUPFER 13,371

VERY HIGH FREQUENCY SUPERHETERODYNE RECEIVER WITH SELF-OSCILLATING MIXER Filed Nov. 20, 1961 INVENTOR.

KARL H. KUPFER United States Patent 3,213,371 VERY HIGH FREQUENCY SUPERHETERODYNE RECEIVER WITH SELF-OSCILLATHNG MIXER Kari Heinz Kupfer, Krefeld, Germany, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Nov. 20, 1961, Ser. No. 153,464 Claims priority, application Germany, Dec. 29, 1960,

26,301 3 Claims. (Cl. 325-440) The invention relates to a very high frequency superheterodyne receiver comprising a self-oscillating mixing tube. The anode of the tube is coupled with a first cavity resonator tuned to the oscillator frequency and the cathode is connected to a coupling loop in a second cavity resonator excited by the input oscillations. The grid of the tube is connected to the outer walls of the preferably adjacent cavity resonators.

In such an apparatus the oscillations of the oscillator are produced in a capacitative feedback circuit (Colpitts circuit). Since the grid is grounded, the cathode has the voltage of the oscillations of the oscillator required for the feedback. Thus a current having the frequency of the said oscillations is produced in the cathode coupling loop these oscillations can be transferred to the conductors conveying the input oscillations, for example by means of an aerial or a series-connected bandpass filter or a preamplifier, so that they may be radiated.

In a receive-r of the kind set forth this radiation may be considerably reduced in a simple manner by providing, in accordance with the invention a first auxiliary coupling loop in the first cavity resonator this first auxiliary coupling loop is connected to .a second auxiliary coupling loop in the second cavity resonator, so that the inductive coupling for the oscillations from the oscillator between the cathode coupling loop and the first cavity resonator is at least substantially neutralised at lea-st for an important part.

The invention will now be described more fully with reference to the drawing, by way of example.

The figure shows the self-oscillating mixing stage of a super-heterodyne receiver for high frequency oscillations, preferably for the range of about 400 to 800 mc./ s.

This stage comprises a first cavity resonator 1, having an inner conductor 2, one end of which is connected by way of a tunable capacitor 3 to the wall 4, surrounding the conductor 2. The other end of the inner conductor 2 is connected by way of a trimmer capacitor 5 also to the wall 4 and by way of a coupling capacitor 6 to the anode of an amplifying tube 7. The tube 7 is arranged so that its grid is approximately coplanar with the wall of the cavity resonator -1. The anode of the tube 7 is connected by way of choke 8 to the positive terminal of a supply source. The negative terminal of the supply source is connected to ground and to the wall 4.

A second cavity resonator 10 is provided adjacent the cavity resonator '1. The inner conductor 11 of cavity 10 is connected by way of a tuning capacitor 12 to the wall 13. The capacitors 12 and 3 are mechanically coupled together. The other end of the inner conductor 11 is connected to the wall by way of a trimmer capacitor 14. The cathode of the tube 7 is connected to a coupling loop 15. The other end of loop :15 is connected to ground by way of a high frequency capacitor 16 and by way of a resistor 17 to the wall 13 (and hence to the negative terminal of the supply source) for producing the desired bias voltage.

The cavity resonator 10 is connected, by way of coupling loop 18, to an antenna 19. A preamplifier may be provided, if desired, between the antenna and the loop 18.

3,213,371 Patented Oct. 19, 1965 The cavity resonator 10 is tuned to the very high frequency signal input oscillations, which are applied to the cathode of the tube 7 by the coupling loop 15. The cavity resonator '1 is tuned to the oscillation frequency of the local oscillator. The anode-to-cath-ode and the grid-cathode capacity of tube 7 constitute a capacitive voltage divider connected as a capacitative feedback circuit to the cavity resonator 1, so that oscillations of the local oscillator frequency are produced. Since the grid of the valve 7 is connected to the wall and therefore has a fixed potential, an alternating voltage of the local oscillator fre quency occurs at the cathode of the valve 7, which produces a current through the cathode coupling loop 15. This current produces in the cavity resonator 10 a field which also acts upon the input coupling loop 1 8. Since the loop 1 8 is connected to the aerial either directly or by way of a preliminary stage, oscillations of the local oscillator fireqeuncy may be applied to the antenna.

In accordance with the invention the first cavity resonator 1 is provided with a first auxiliary coupling loop 21, and the second cavity resonator 10 is provided with a second coupling loop 22 these auxiliary loops are connected to each other. Consequently, the auxiliary coupling loop 21 transfers oscillations from the local oscillator in cavity resonator 1 to the second auxiliary coupling loop 22. These transferred oscillations produce a field of local oscillator frequency in the second cavity resonator 10. The auxiliary coupling loops 21 and 22 are approximately parallel with the inner conductors 2 and -11 and their ends nearest the tube 7 are connected to each other. The field of the second coupling loops 22 is in phase opposition to the field of local oscillator frequency produced by the cathode coupling loop 15, so that the inductive coupling at the first cavity resonator 10 and particularly of the input coupling loop 18 is at lea-st substantially neutralised.

The second auxiliary coupling loop 22 is preferably arranged in the proximity of the cathode coupling loop 15. The two coupling loops 22 and '15 may be twisted together. The first auxiliary coupling loop 21 may be con nected directly or by the stray capacity 23, indicated by dashed lines in the drawing, to the wall of the cavity resonator 1. Similarly, the second auxiliary loop 22 may be connected directly or by -way of stray capacity 24, as shown by dashed lines, to the wall of cavity resonator 10. -By adjusting the distance and/or the length of the first coupling loop 21 with respect to the inner conductor 2 of the first cavity resonator 1 the amplitude of the neutralizing oscillations can be varied.

Instead of using cavity resonators of known type, use may .be made of hollow waveguides of any shape. The invention also provides advantages, if instead of an electron tube any other, prefer-ably amplifying, element is used for mixing purposes, between two cavity resonators in which a transmission or oscillators from the local oscillator to the input cavity resonator 10* occurs.

What is claimed is:

1. A self oscillating mixing circuit comprising first and second tunable resonant cavities, a source of signal oscillations, means applying said signal oscillations to said second cavity, an amplifier device having input, common and output electrodes, first loop means in said second cavity for coupling said signal oscillations to said input electrode, means connecting said common elect-rode to a wall of said cavities, means regeneratively coupling said output electrode to said first cavity whereby local oscillations are produced in said firs-t cavity and said local oscillations appear at said input electrode in said second cavity, and means for substantially neutralizing said local oscillations in said second cavity comprising a second coupling loop in said second cavity, a third coupling loop in said first cavity, and means for interconnecting said second and third coupling loops.

2. A self oscillating mixing circuit comprising first and second cavity resonators, a source of input signals, means for tuning said second cavity resonator to the frequency of said signals, an amplifier device having input, common and output electrodes, means for app-lying said signals to said second cavity resonator, first loop means in said second cavity resonator connected to said input electrode for coupling said input signals to said device, means connecting said common elect-rode to a wall of said first and second cavity resonators, means for lregeneratively connecting said output electrode to said first cavity [resonator whereby local oscillations are produced at a frequency determined by the tuning of said first cavity resonator,

second and third coupling loops in said second and first cavity resonators respectively, and means for interconnecting said second and third coupling loops, whereby oscillations of the frequency of said local oscillations are substantially neutralized in said second cavity resonator.

3. A self oscillating mixing circuit comprising first and second cavity resonators, a source of input signals, means for tuning said second cavity resonator to the frequency of said signals, means for applying said signals to said second cavity resonator, an electron discharge device having a cathode, a grid and an anode, means connecting said grid to a wall of said first and second cavity resonators, means regeneratively coupling said anode to said first cavity resonator whereby local oscillations are produced at a frequency determined by the tuning of said first cavity resonator, first loop means in said second cavity resonator connected to said cathode for coupling said signals to said cathode, whereby local oscillations at said cathode are coupled to said second cavity resonator, and means for substantially neutralizing said local oscillations in said second .cavity resonator comprising second and third coupling loops in said second and first cavity resonators respectively, and means for interconnecting said second rand t-hind coupling loops.

References Cited by the Examiner UNITED STATES PATENTS 2,039,634 5/36 Clay 325--436 2,909,73 1' 10/59 Franck 33197 2,962,586 11/60 Maurer 325445 DAVID G. REDINBAUGH, Primary'Examiner. 

1. A SELF OSCILLATING MIXING CIRCUIT COMPRISING FIRST AND SECOND TUANBLE RESONANT CAVITIES, A SOURCE OF SIGNAL OSCILLATIONS, MEANS APPLYING SAID SIGNAL OSCILLATIONS TO SAID SECOND CAVITY, AN AMPLIFIER DEVICE HAVING INPUT, COMMON AND OUTPUT ELECTRODES, FIRST LOOP MEANS IN SAID SECOND CAVITY FOR COUPLING SAID SIGNAL COSCILLATIONS TO SAID INPUT ELECTRODE, MEANS CONNECTING SAID COMMON ELECTRODE TO A WALL OF SAID CAVITIES, MEANS REGENERATIVELY COUPLING SAID OUTPUT ELECTRODE TO SAID FIRST CAVITY WHEREBY LOCAL OSICLLATIONS ARE PRODUCED IN SAID FIRST CAVITY AND SAID LOCAL OSCILLATIONS APPEAR AT SAID INPUT ELECTRODE IN SAID SECOND CAVITY, AND MEANS FOR SUBSTANTIALLY NETURALIZING SAID LOCAL OSCILLATIONS IN SAID SECOND CAVITY COMPRISING A SECOND COUPLING LOOP IN SAID SECOND CAVITY, A THIRD COUPLING LOOP IN SAID FIRST CAVITY, AND MEANS FOR INTERCONNECTING SAID SECOND AND THIRD COUPLING LOOPS. 